In the prior art, there exists several structures for pressure transducers. In particular, in the prior art which relates to pressure transducers which measure microstrain of a diaphragm, there exists several structures each with their own problems. The first such structure was the unbonded strain gauge-type pressure transducer. This type of pressure transducer utilizes very fine wires together with sapphire rods arranged in a machined housing having various tie points and curved portions. Such a pressure transducer is very complex to manufacture and is exceedingly fragile.
A second type of pressure transducer involves the so-called bonded strain gauge-type utilizing very small semiconductor or foil strain gauges. Since the strain gauges are exceedingly small and the attachment wires on the strain gauges are even smaller and are typically made from a soft metal such as gold, a means must be provided within the pressure transducer housing so that the exceedingly fine wires from the strain gauges can be connected to the output cable of the pressure transducer. Such means have included solder tabs bonded to the inside of the pressure transducer housing and a miniature rigid circuit board provided within the transducer housing and bonded about its periphery to the inside surface of the transducer housing with epoxy or the like. Such structures as the solder tabs or the rigid circuit boards have a problem in that there exists induced microstrain inherent in their own structure. In particular, the epoxy used to bond either the solder tabs or the circuit board to the inside surface of the transducer housing has a different coefficient of expansion than the material that the housing is made from. Since the epoxy has a different temperature coefficient of expansion than the material of the housing and since such structures typically require a relatively large amount of epoxy to bond either the solder tabs or the rigid circuit board, the epoxy expands at a different rate than the housing thereby inducing microstrain into the structure and affecting the accuracy of the pressure transducer. Furthermore, since the miniature rigid circuit board is usually coupled directly to the output cable of the pressure transducer, strains applied to the cable are also transmitted via the rigid circuit board to the structure thereby also affecting the accuracy of the reading of the pressure transducer.
Accordingly, it is a general object of the present invention to provide a structure for a very small pressure transducer which is relatively insensitive to problems created by the thermal coefficience of expansion of the various materials utilized in the transducer, stresses created by the means for mounting the pressure transducer, the extreme stresses that may be encountered during handling and use of the transducer and the extremely small physical dimensions.
It is yet another object of the present invention to provide a structure for a pressure transducer which allows the pressure transducer to be easily manufactured using acceptable production techniques.